This invention relates to semiconductor wafer holding and, in particular, to a wafer holding assembly for securing semiconductor wafers as the wafers are manipulated in a semiconductor processing machine.
Semiconductor processing machines are arranged in a semiconductor production line for performing a series of processing steps resulting in the fabrication of integrated circuits in and on a device-side surface of a substrate or semiconductor wafer. Semiconductor processing machines are designed to manipulate and hold a succession of wafers, particularly silicon wafers, within a process chamber during each processing step. As the wafers are manipulated by the processing machine, the wafers are held in various vertical, horizontal, and inverted orientations required by the wafer-handling process of the processing step. The wafers are usually secured in wafer holders that apply a mechanical clamping force which permits non-horizontal manipulation. To limit damage to integrated circuits on the device-side or backside surface treatments of the substrate, wafer holders have been developed that clamp the substrate along a narrow annular ring or exclusion zone inside of the peripheral edge of the wafer. Conventional wafer holders of this type utilize an annular clamp ring and a plurality of moveable latches, which typically contact the wafer only within the exclusion zone, arranged about the circumference of the wafer holder or clamp ring. A conventional latch typically engages the semiconductor wafer with a roller that rolls over the rim of the wafer and across the wafer surface. When the latches are engaged, a clamping force is applied to the wafer surface that captures the semiconductor wafer between the clamp ring and the latches.
Semiconductor wafers are relatively delicate and are susceptible to damage as a result of clamping by the wafer holder. Conventional latches are known to apply an undue latching pressure to the rim of the wafer and the wafer surface. The excessive latching pressure may cause mechanical damage, such as chipping or abrading, as the rollers of the latches roll or slide over the rim of the wafer As the latches move to a latched position, excessive latching pressure applied by the rollers to the surface of the semiconductor wafer may produce scoring or abrasion. Material removed from the semiconductor wafer creates debris assuming the form of small particles. Debris particles residing on the wafer surface during processing produce particulate contamination that adversely affects the operating characteristics of the affected integrated circuits. Moreover, the particle contamination reduces the product yield of functional integrated circuits by rendering affected circuits defective. Particle contamination is believed to be responsible for the vast majority of the product yield loss in a production line. Therefore, it is essential to eliminate possible sources of particles to reduce particle contamination of substrates that would, if unabated, cause defective integrated circuits.
Conventional latches have exposed moving parts, such as the rollers, that tend to accumulate a coating of material from processing steps that apply a layer of a coating material, such as physical vapor deposition. As the coating material accumulates on the moving parts, the latch can experience malfunctions and operational failures. As a result, the process chamber of the semiconductor processing machine must be opened and the affected latch either cleaned or replaced. The maintenance results in lost production time which idles the processing machine and can potentially idle an entire production line during the maintenance.
With growing requirements for improved reliability and increased device yields, an objective of this invention is to provide a latch for use with a wafer holder of a semiconductor processing machine that can secure semiconductor wafers of varying thickness to a clamp ring without damaging or otherwise adversely affecting the wafer surface and that can also minimize particle generation within the process chamber during the latching process.
The forgoing objective has been accomplished, according to the present invention, by providing a wafer holder for a semiconductor processing machine having a latch assembly that reduces or eliminates the contact pressure or load applied to the wafer rim and the wafer surface as the latch assembly is actuated between unlatched and latched conditions. The wafer holder of the present invention comprises a support frame, a clamp ring attached to the support frame, and plurality of latch assemblies mounted to the clamp ring. The support frame has an inner peripheral edge that defines a first circular opening having a central axis. The first circular opening is diametrically larger than the diameter of the wafer. The clamp ring has a face facing the support frame and an inner peripheral flange defining a second circular opening. The second circular opening is diametrically smaller than the diameter of the wafer and is substantially centered with the central axis. The inner peripheral flange has a wafer-engaging surface for contacting a first surface of the wafer when the wafer is inserted into the first opening and a plurality of inclined surfaces located adjacent the central opening and positioned at spaced angular positions about the central axis. Each of the plurality of inclined surfaces ascends radially outwardly away from the central axis. The plurality of latch assemblies are mounted to the clamp ring at one of the spaced angular positions. Each latch assembly includes a mounting post mounted to the inner peripheral flange of the clamp ring and a latch body rotatably carried on the mounting post. The latch body is rotatable through a pivot arc between a latched position and an unlatched position. A clamping roller assembly and a supporting roller assembly are mounted to the latch body. The clamping roller assembly has a resiliently-biased first rolling element adapted to apply a clamping force to a second surface of the wafer operable to capture the wafer between the rolling element and the wafer-engaging surface of the inner peripheral flange when the latch body is in the latched position. The clamping roller assembly has a resiliently-biased second rolling element that rollingly engages the inclined surface. The rolling engagement between the second rolling element and the inclined surface separates the first rolling element from the second surface of the wafer in a non-contacting manner until the latch body is substantially in the latched position.
According to the present invention, a plurality of latch assemblies of the present invention may be provided as a retrofit kit to replace the existing latch assemblies of a wafer holder. Alternatively, a clamp ring may be included with the plurality of latch assemblies of the present invention as a retrofit kit for a wafer holder to replace the existing clamp ring and latch assemblies. The latch assemblies of the present invention are compatible with the existing hardware and controls of many semiconductor processing machines that may be candidates for the retrofitting operation. As a result, the semiconductor processing machine can be retrofitted with latch assemblies of the present invention without substantial hardware changes and without modifying the control software of the machine.
By virtue of the foregoing, there is provided a latch assembly for a wafer holder that engages and secures a semiconductor wafer for processing. The latch assembly contacts the wafer surface and applies a clamping pressure only when the latch body is angularly proximate the latched position or, preferably, fully in the latched position. As a result, the rolling element of the latch assembly is separated by a gap from the wafer surface as the latch body is rotated between the unlatched and latched positions. Because the latch assembly does not contact the wafer surface unless in or near a latched position, the latch assemblies of the present invention significantly reduce or eliminate particulate matter that would otherwise be created by conventional latch assemblies that abrade and chip the wafer surface. The present invention reduces the force that need be applied to pivotably actuate the latch assemblies by incorporating roller bearings between the latch body and support member. The present invention provides a wafer holding and securing system that is compatible with, and that can be retrofitted to, existing semiconductor processing machines that lack such capabilities. The present invention may be retrofitted to an existing semiconductor processing machine with little or no impact on the hardware of the processing machine and with minimal impact on the operating software of the processing machine.
When holding a semiconductor wafer during a deposition process, the latch assembly of the present invention substantially conceals the rolling elements of the roller assemblies and the roller bearings between the latch body and support member from the flux of coating material depositing on the exposed surface of the wafer. Therefore, the roller assemblies and roller bearings do not require frequent cleaning or replacement.